Micropropagation, also known as axillary bud propagation or in vitro asexual propagation, is one of a number of methods known in the art for the propagation of desirable species or varieties of plants. Other traditional methods of asexual propagation include greenhouse and field propagation of plant cuttings. There are many advantages, however, which favor micropropagation as a propagative method of choice. One advantage is that a plant which has a known and desirable phenotype can be chosen as the source of cells, and, in accordance with micropropagation techniques, these cells can be rapidly cultured into many genetically uniform plantlets. The resulting plantlets may then be cultivated into entire plants possessing roots and shoots. Thus, in accordance with this technique, plants with the same desirable phenotype as the parent can be mass produced, potentially at costs comparable to and often more quickly than standard greenhouse or field methods of asexual propagation.
The propagation of plants under sterile aseptic conditions has been used as cost effective means for the mass propagation of certain plants. An important consideration of this technology is the ability to add value to plants being propagated. In many cases value is added by assuring uniformity of product, and products that are free of bacterial, fungal, viral, or insect pests.
Commercial propagation of roses is normally carried out by budding or grafting of a specific shoot cutting, or scion, onto an established wild rose root stock. In recent years numerous publications have dealt with the propagation of roses though tissue culture. Examination of the literature reveals that different varieties and types display greatly varying nutrient and hormone requirements. Indeed, the process of producing plants from explants or plant tissues, however, requires the development of a culture medium and protocol suitable for the particular type of plant tissue. Various media and procedures have been attempted, but only some have been met with success. For this reason, most commercial growers of roses still propagate rose plants by traditional means.
For example, Hasegawa, J. Amer. Soc. Hort. Sci. 1980 105, 216-220, the disclosures of which are hereby incorporated by reference in their entirety, reported that media developed for the climbing rose Improved Blaze allowed significant growth of three miniature rose varieties but not for all hybrid tea roses. Khosh-Khui and Sink, J. Hort. Sci. 1982 57, 315-319 and Khosh-Khui and Sink, Scientia Horticulturae 1982 17, 371-376, the disclosures of which are hereby incorporated by reference in their entirety, found that plant growth regulator requirements for multiplying the R. hybrida cultivars, Tropicana and Bridal Pink differed considerably from those of two old world species R. damascena and R. canina.
To optimize growth conditions most studies have focused on variations in the concentrations of certain growth regulators, Hasegawa, supra. A few studies have investigated the effect of certain other inorganic or organic components. For example, Khosh-Khui and Sink, supra. investigated the effect of explant orientation, explant size and lighting on the growth of new and old world species. Bressan et al., J. Amer. Soc. Hort. Sci. 1982 107, 979-990, the disclosures of which are hereby incorporated by reference in their entirety, investigated the effect of bud position, temperature, hours of light per day, Murashige and Skoog ingredient concentrations, and weeks in culture between transfers.
Despite some success in developing suitable culture media and culturing processes, new and/or better media and methods, particularly for commercially significant roses, are needed. Toward this end, the present invention is directed to the development of media useful for the propagation of roses and for induction of flowering in vitro.